Filtering devices that are percutaneously placed in the vena cava have been available for over thirty years. A need for filtering devices arises in trauma patients, orthopedic surgery patients, neurosurgery patients, or in patients having medical conditions requiring bed rest or non-movement. During such medical conditions, the need for filtering devices arises due to the likelihood of thrombosis in the peripheral vasculature of patients wherein thrombi break away from the vessel wall, risking downstream embolism or embolization. For example, depending on the size, such thrombi pose a serious risk of pulmonary embolism wherein blood clots migrate from the peripheral vasculature through the heart and into the lungs.
After deployment of a generally conical filter in a patient, the filter will generally become anchored to the wall of the vena cava or other body lumen in which it was delivered. Proliferating intimal cells begin to accumulate around the filter parts which contact the wall of the vessel. After a length of time, such ingrowth prevents removal of the filter without risk of trauma so that the filter is permanently left in the patient.
Moreover, conventional filters commonly become off-centered or tilted with respect to the hub of the filter and the longitudinal axis of the vessel in which it has been inserted. As a result, the filter including the hub and the retrieval hook engage the vessel wall along their lengths and potentially become endothelialized therein. As a result, the filter becomes a permanent implant in a shorter time period than otherwise.
After filtering is complete, or after filtering is no longer desirable or effective, it may be desirable to retrieve the filter from the vena cava. If the filter has tilted or has otherwise become ingrown into the tissue, retrieval according to known methods may become more difficult. Moreover, during retrieval, emboli that have become trapped in the filter may become dislodged and can re-enter the bloodstream, which is undesirable.
Accordingly, improvements may be made related to the retrieval of vena cava filters.